1. Field of the Invention
The object of the present invention is a system for the dynamic correction of the orientation of a light source mounted on a motor vehicle, as well as a correction method using such a system. The system according to the invention is an optoelectronic system that makes it possible to instantaneously correct faulty orientation of a light beam emitted by a headlight device on the vehicle in question, in response to sudden variations in the attitude of the vehicle.
The field of the invention is in general terms that of lighting devices for vehicles travelling on the road such as for example cars and vehicles of the heavy goods type. More precisely, the invention concerns the orientation of the headlights of these vehicles.
2. Description of the Related Art
Optoelectronic correction means a correction performed by virtue of components that are transducers passing from electronic to optical or from optical to electronic. Currently all the vehicles travelling on the road have a device for illuminating the road used particularly at night or during bad weather. Conventionally there exists on motor vehicles in particular two types of lighting: lighting called “main beam”, which illuminates the road entirely over a long distance, and lighting called “dipped beam”, which illuminates the road over a short distance in order to avoid dazzling the drivers of the vehicles liable to come in the opposite direction or travelling in front.
In the case of dipped lighting, the range of the lighting is adjusted in particular by orienting the headlights in the vertical plane. Conventionally, the orientation of the light beam emitted by dipped headlights is adjusted by specialists, in particular automobile mechanics, according to information given by the manufacturer of the lighting device. The angle of orientation of the light beam is given by the manufacturer as a percentage of radians. This angle of orientation of the light beams is given for a vehicle in a standard position, which designates the position in which the chassis of the vehicle is substantially parallel to the road, that is to say the position in which the angle formed by the vehicle chassis with the horizontal plane is flat. It is then said that the attitude of the vehicle is flat. In general terms, the attitude of a vehicle corresponds to a measurement of the inclination of the vehicle with respect to the plane of the road that it is following.
However, it is known that the attitude of the vehicle may be modified according to the situation in which the vehicle is, in particular according to the loading of the vehicle. This is because, when the vehicle is highly loaded, the rear of the vehicle is lowered, which means that the front of the vehicle is raised. The vehicle is therefore no longer parallel to the road. In this case, the light beams from the dipped headlights of the vehicle are directed towards the horizon instead of being directed towards the road. They may then dazzle the drivers of vehicles coming in the opposite direction or travelling in front.
It will thus be understood that the initial adjustment of the dipped headlights, carried out for a vehicle in the standard position, is not correct when the attitude of the vehicle is no longer flat.
To resolve this drawback, some vehicles are equipped with an automatic correction system fixed to the vehicle chassis. This system comprises sensors placed on the front and rear axles of the vehicle and which each measure the difference in height between the position of the wheel and the chassis, according to the loading of the vehicle. A small computer integrated in the automatic correction system determines the attitude of the vehicle and gives information to small motors that orient the headlights. However, this system has drawbacks. This is because the sensors are placed at a short distance from the wheels, that is to say at places that are difficult for a person or robot to access when the vehicle is being manufactured. Thus the operation of fitting the sensors, during the manufacture of the vehicle, requires great precision and consequently considerable investment in time and money. In addition, these sensors are subjected to splashing of water, gravel and other elements that may be situated on the road. The connections to these sensors and the sensors themselves must therefore be robust in order to withstand such splashing.
To meet these drawbacks, optoelectronic correction systems have recently been proposed. For example, the French patent published under the number FR 02 15874, which is equivalent to U.S. Publication Number 2004/0178738, proposes a system for controlling the orientation of the headlights of a vehicle from a camera and a specific point in the light beam, according the attitude of the vehicle. This system consists of fixing a camera to the vehicle, or using a camera already in place in the vehicle, in order to film the road extending in front of the vehicle. An image processing unit then processes at least one image in order to determine the horizon line of the scene situated in front of the vehicle. From this horizon line, it is possible to determine a specific point in the scene and then to adjust the headlight until a specific light spot emitted by a light emission source mounted on the headlight reflector is merged with the specific point. In certain embodiments, the light emission source is of the infrared type, just like the camera used.
FIG. 1 depicts schematically an example embodiment of the system 100 controlling the orientation of a vehicle headlight according to the patent published under FR 02 15874. The scene unfolding in front of the running vehicle is filmed by a camera 101 oriented towards the front of the vehicle. In other examples, the camera 101 is oriented towards the rear of the vehicle, without the system described here having to undergo any significant modifications. The camera 101 can possibly be used for implementing functions other than those relating to the object of the patent FR 02 15874. The camera 101 is advantageously adapted to photographing at night, for example by being of the infrared type. A device for static correction for correcting of the orientation of light source in response to variations in the attitude of the vehicle 102, including in particular a first unit for processing the images acquired—or captured—by the camera 101, produces a first set of information relating to a static measurement of the vehicle attitude, that is to say an average measurement of the attitude over a period of several seconds.
A device 103 for controlling the rotation of a light source 104 controls the orientation of the headlights 104A and 104B in a suitable fashion according to the information received from the device for static correction in response to sudden variations in the attitude of the vehicle 102.
The headlight 104A emits a first light beam 105A towards the front of the vehicle. The headlight 104B emits a second light beam 105B which is able to project a specific light spot onto the road. The connectedness of the headlights 104A and 104B enables them to move simultaneously from an angular point of view. The movements of the light beams 105A and 105B result in a light sweep 106 of predetermined amplitude.
The static correction device is characterized by a long time constant. Long time constant means the fact that the device 102 produces information from images that are spaced apart in time, even though an economically accessible camera has an image acquisition frequency of around 30 images per second. This is because the road scene filmed is often disturbed, for example by the presence of other vehicles appearing and disappearing from the captured images, or by the existence of disturbing environments such as pebbles and irregularities on the roadway, which generate uncertainties in the calculation of the horizon line and impose a relatively long filtering time compared with the image sampling frequency of the camera.
Thus such a system makes it necessary to accept less great precision in order to obtain a shorter response time, without ever attaining a satisfactory response time, for example around 0.2 seconds, desirable when a rapid variation in attitude is observed. This is why the system presents risks of error that may lead to uncomfortable or even dangerous situations for the driver, these situations being related to excessive and/or ill-timed correction amplitudes. It is moreover totally unsuited to a dynamic correction in response to variations in the attitude. Such a dynamic correction designates a correction for compensating the attitude that results in an intervention on the orientation of at least one light source, which is carried out very rapidly, that is to say in times of around 0.2 seconds. Such a correction makes it possible to adapt to the rapid variations in attitude that are observed during abrupt acceleration or braking stages.
What is needed, therefore, is a system and method that provides dynamic correction of the orientation of a light source and that overcomes one or more problems of the prior art.